Fix thread safety of http writer (#11464)

Author: kumaraditya303

CHANGES/11464.feature.rst

@@ -0,0 +1 @@
+Implemented support for free-threading builds of CPython -- by :user:`kumaraditya303`.

Makefile

@@ -59,14 +59,14 @@ aiohttp/_find_header.c: $(call to-hash,aiohttp/hdrs.py ./tools/gen.py)
 # Special case for reader since we want to be able to disable
 # the extension with AIOHTTP_NO_EXTENSIONS
 aiohttp/_websocket/reader_c.c: aiohttp/_websocket/reader_c.py
-	cython -3 -o $@ $< -I aiohttp -Werror
+	cython -3 -X freethreading_compatible=True -o $@ $< -I aiohttp -Werror
 
 # _find_headers generator creates _headers.pyi as well
 aiohttp/%.c: aiohttp/%.pyx $(call to-hash,$(CYS)) aiohttp/_find_header.c
-	cython -3 -o $@ $< -I aiohttp -Werror
+	cython -3 -X freethreading_compatible=True -o $@ $< -I aiohttp -Werror
 
 aiohttp/_websocket/%.c: aiohttp/_websocket/%.pyx $(call to-hash,$(CYS))
-	cython -3 -o $@ $< -I aiohttp -Werror
+	cython -3 -X freethreading_compatible=True -o $@ $< -I aiohttp -Werror
 
 vendor/llhttp/node_modules: vendor/llhttp/package.json
 	cd vendor/llhttp; npm ci

aiohttp/_http_parser.pyx

@@ -1,5 +1,3 @@
-#cython: language_level=3
-#
 # Based on https://github.com/MagicStack/httptools
 #
 

aiohttp/_http_writer.pyx

@@ -8,7 +8,6 @@ from libc.string cimport memcpy
 from multidict import istr
 
 DEF BUF_SIZE = 16 * 1024  # 16KiB
-cdef char BUFFER[BUF_SIZE]
 
 cdef object _istr = istr
 
@@ -19,16 +18,17 @@ cdef struct Writer:
     char *buf
     Py_ssize_t size
     Py_ssize_t pos
+    bint heap_allocated
 
-
-cdef inline void _init_writer(Writer* writer):
-    writer.buf = &BUFFER[0]
+cdef inline void _init_writer(Writer* writer, char *buf):
+    writer.buf = buf
     writer.size = BUF_SIZE
     writer.pos = 0
+    writer.heap_allocated = 0
 
 
 cdef inline void _release_writer(Writer* writer):
-    if writer.buf != BUFFER:
+    if writer.heap_allocated:
         PyMem_Free(writer.buf)
 
 
@@ -39,7 +39,7 @@ cdef inline int _write_byte(Writer* writer, uint8_t ch):
     if writer.pos == writer.size:
         # reallocate
         size = writer.size + BUF_SIZE
-        if writer.buf == BUFFER:
+        if not writer.heap_allocated:
             buf = <char*>PyMem_Malloc(size)
             if buf == NULL:
                 PyErr_NoMemory()
@@ -52,6 +52,7 @@ cdef inline int _write_byte(Writer* writer, uint8_t ch):
                 return -1
         writer.buf = buf
         writer.size = size
+        writer.heap_allocated = 1
     writer.buf[writer.pos] = <char>ch
     writer.pos += 1
     return 0
@@ -125,8 +126,9 @@ def _serialize_headers(str status_line, headers):
     cdef Writer writer
     cdef object key
     cdef object val
+    cdef char buf[BUF_SIZE]
 
-    _init_writer(&writer)
+    _init_writer(&writer, buf)
 
     try:
         if _write_str(&writer, status_line) < 0: